Trim parts, such as foam backed instrument panel pads, often have a simulated decorative stitching molded directly into the vinyl skin or outer layer at the time the resilient foam backing is molded thereto. Actual stitches on the visible outer layer may provide a different aesthetic appearance and color contrast to the trim part. However, it is not practical to actually stitch the outer layer, either manually or on a sewing machine and then mold the foam backing to it, because of difficulties of aligning the stitched layer in the mold, foam leakage through the stitch holes, and the cost of scrapping the part after the most labor intensive step, the stitching, has been completed.
Therefore, the decorative actual stitching should be applied to the completed trim part. This presents several problems in trim parts, such as instrument panels, which are generally irregular in thickness and shape, may have a foam back of convoluted shape, and may have inserts in the foam which make it impossible to pierce the part with a needle, either manually or by sewing machine. Work access is limited only to the outer surface of the outer layer.
It is known to provide actual loop type stitches which extend from the outer side of a material. The material must have generally uniform thickness, be relatively thin, and must be stretched tightly across a frame while being stitched from the inner side. The apparatus includes a hollow needle extending from an enlarged handle and having a central thread passage and a slanted tip with a trailing side and a leading side. The trailing side includes a sharp piercing point and an eye therethrough just above the point. Thread is fed through the central passage with a free end passing out through the eye. As the needle is punched through the material from the inner side, the thread catches on the edge of the hole formed by the needle in the material and additional thread is pulled through the passage and the eye, until the handle engages the inner side of the material. As the needle is pulled back through the material, the eye catches the thread and pulls it back to create a loop having a length half the distance the needle was originally punched through the material. When the needle is pulled back through the material, the tip must be dragged across the inner side of the material without raising it above the surface, for a short distance and then punched through the material to again repeat the process. This process leaves a row of short, flat stitches on the inner or non-visible side of the material and loop type stitches on the outer or visible side. Such a process cannot be used with trim parts such as instrument panels because it requires the complete penetration of the part from the inner side. If the needle is punched only partially through a relatively thick trim part, the thread is pulled back out again by the needle eye when the needle is withdrawn.